(1) Field of the Invention
The present invention relates to a structure for dissipating heat generated by an electronic component mounted on a printed circuit board through a heat transfer member embedded in the printed circuit board.
(2) Description of Related Art
There are proposed various techniques for embedding a heat transfer member in a printed circuit board in order to dissipate heat generated by an electronic component mounted on the printed circuit board.
For example, according to each of Patent Documents 1 to 3, a heat transfer member made of metal such as copper is embedded in an insulating layer of a printed circuit board, and an electronic component that generates heat is mounted above the heat transfer member.
According to Patent Document 1, a wiring pattern is provided on each of upper and lower surfaces and inside of the printed circuit board, and the electronic component is mounted on the wiring pattern on the upper surface which is electrically connected to the heat transfer member. A lower surface of the heat transfer member is covered with the highly thermally conductive insulating layer, and a heat dissipation member is provided so as to be in contact with a lower surface of the insulating layer. Heat generated by the electronic component is thereby transferred to the heat dissipation member through the wiring pattern on the upper surface, the heat transfer member and the highly thermally conductive insulating layer, and is dissipated from the heat dissipation member to the outside.
According to Patent Document 2, a lower surface of the heat transfer member is exposed from the insulating layer of the printed circuit board, and the electronic component is mounted above the heat transfer member through the highly thermally conductive insulating layer and a wiring pattern. Heat generated by the electronic component is thereby dissipated from the exposed lower surface of the heat transfer member to the outside through the wiring pattern, the highly thermally conductive insulating layer and the heat transfer member.
According to Patent Document 3, upper and lower surfaces of the heat transfer member are exposed from the insulating layer of the printed circuit board, and the electronic component is mounted above the heat transfer member through solder. Moreover, a heat dissipation member is provided on lower surfaces of the printed circuit board and the heat transfer member through a heat transfer material such as heat dissipation grease. Heat generated by the electronic component is thereby transferred to the heat dissipation member through the solder, the heat transfer member and the heat transfer material, and is dissipated from the heat dissipation member to the outside.
Now, as disclosed in Patent Document 3, for example, the heat transfer member can be formed easily into a predetermined shape by stamping out a metal plate in a thickness direction (stamping). In this case, one outer surface orthogonal to the thickness direction of the heat transfer member becomes a protruding surface having a curved portion (a so-called “shear droop”) caused at its edge, and the other outer surface orthogonal to the thickness direction of the heat transfer member becomes a recessed surface having a protruding portion (a so-called “burr”) caused at its edge.
According to Patent Document 3, in order to prevent the solder from flowing out from between the heat transfer member and the electronic component, the recessed surface of the heat transfer member is exposed from the upper surface of the printed circuit board so as to face the electronic component. Moreover, the protruding surface of the heat transfer member is exposed from the lower surface of the printed circuit board so as to face the heat dissipation member.
Moreover, outer shapes of a metal substrate as disclosed in Patent Documents 4 to 6 and a metal stiffener as disclosed in Patent Document 7 are also formed by stamping out a metal plate in a thickness direction. Then, one outer surface orthogonal to the thickness direction thereof becomes a protruding surface having a shear droop, and the other outer surface becomes a recessed surface having a burr.
According to each of Patent Documents 4 and 5, the recessed surface of the metal substrate is placed on an upper surface of a heat dissipation member through heat dissipation grease or solder. According to Patent Document 7, the recessed surface of the metal stiffener is placed on an upper surface of a wiring board through an adhesive. According to Patent Document 6, a groove is provided on an upper surface of the metal substrate, and the metal substrate is stamped out at the groove, and a burr is caused inside of the groove. Then, a wiring pattern is provided on the upper surface of the metal substrate except for the groove, and an electronic component is mounted.